1. Field of the Invention
The present invention relates generally to an apparatus and process for medical imaging. More particularly, the present invention relates to medical X-ray imaging systems such as an X-ray computer tomography scanner that includes a subject restraining mechanism and a process for operating thereof.
2. Description of the Prior Art
Computerized tomography is a modern non-invasive technique developed for revealing internal organs and tissues of a human body in cross-section to aid in medical diagnosis, examination, surgery, etc. Essentially an X-ay beam is passed through an imaging subject, e.g. human body, at one location. Part of the X-beam is attenuated by the tissue of the imaging subject, with the remainder of the X-ray beam transmitting through the subject and projecting onto a detector. The detector measures the intensity of the beam transmitting through the imaging subject. The detector then sends electronic signals responsive to the X-ray beam to a computer which calculates and stores the beam intensity for the purpose of reconstructing a graphic image of the subject.
For a measurement at a different location on the subject, the X-ray beam is rotated in one plane to a different angular position and similar measurements are made and recorded. This process is continued for 360 degrees, at which time the computer utilizes the combined measurements recorded to reconstruct a two dimensional image of a cross-sectional slice of the imaging subject. The X-ray beam is then transversely moved by moving the subject and the process repeated to develop another picture of a new cross-sectional slice of the subject. By taking a plurality of such transversely spaced slices and stacking one on top of the other, a three dimensional image of a portion of the subject could be constructed by the computer.
The earliest computerized axial tomography used a pencil beam with a single detector. The beam and the detector were simultaneously rotated and then linearly translated to develop an appropriate scan of the subject. To reduce scanning time a fan-shaped beam replaced the pencil beam and multiple detectors arrayed in an arc were used instead of a single detector. Various detector arrays and detector-beam movements were subsequently developed to increase the speed of the scanning process.
More recent developments in computer tomography employ a source which generates a cone-shaped X-ray beam, instead of the fan-shaped beam, and a two dimensional detector array, instead of a linear array of detectors. This configuration allows the scanning of multiple slices at once. In related industrial applications of computerized tomography disclosed in U.S. Pat. No. 5,023,895, issued to McCroskey, et. al., the use of a cone beam in computer tomography is further improved by rotating a turntable where an object is placed.
None of these systems provide a simple, inexpensive device for scanning the internal organs of a human being. None of these systems provide an acceptable means for restraining a person to prevent movements during the scanning process.
The present invention provides a relatively inexpensive and compact computer tomography system and a process of using the same that rapidly and accurately creates an image of the section of a person under examination.
One object of the invention is to provide an improved medical computer tomographic system which can rapidly produce accurate images of medical subjects.
Another object of the invention is to provide an improved medical computer tomographic system which can produce accurate images of medical subjects inexpensively.
Another object of the invention is to provide an improved medical computer tomographic system which can produce accurate images of medical subjects without unnecessary discomfort to the subject.
Another object of the invention is to provide an improved medical computer tomographic system which can produce accurate images of medical subjects without performing extensive complex calibration to the x-ray source and detector in the conventional computer tomographic systems.
Yet another object of the invention is to provide an improved medical computer tomographic system which can produce accurate images of medical subjects requiring less complexity of equipment and operation than existing systems.
Briefly, the preferred embodiment includes a source, a detector array, a support structure, a mechanism for rotating the support structure, a restraining mechanism, and an imaging mechanism. The source projects a roughly cone shaped beam of X-ray radiation on to a subject such that a portion of the beam transmits through the subject and projects on to the detector array. The support structure supports the subject and rotates the subject about an axis perpendicular to and intersecting with the X-ray beam such that the X-ray beam continues to project on the subject throughout the support units rotation. The restraining mechanism is attached to the support structure and restrains the subject from unnecessary movement during rotation. The portion of the X-ray beam that transmits through the subject projects on to the detector array. The detector array detects the X-ray beam transmitted through the subject and is operative to generate an electronic signals responsive to the beam transmitted through the subject. The imaging mechanism receives the electronic signals from a detector within the detector array and is operative to generate an image responsive to the electronic signals.
One advantage of the invention is its simple design which requires less equipment than other medical computer tomography scanners and, hence, less maintenance. The system of the present invention does not require the bulky and expensive equipment needed to rotate the detector and X-ray source nor the equipment necessary to feed the subject through the tomography scanner.
Another advantage is that the invention scans the subject in one revolution, whereas prior art systems require multiple rotations due to their use of fan-shaped x-ray beams as opposed to cone-shaped x-ray beams. By using a cone-shaped x-ray beam the present invention eliminates the need to feed the subject through the scanning system.
Yet another advantage of the invention is low cost. The system does not require the expensive mechanism necessary to move the detectors and x-ray source, nor does it require as much calibration as systems that rotate the x-ray source and detector.
Yet another advantage of the invention is the simplified calibration process required to calibrate imaging to compensate for variation produced by the movement of the source and detector. The invention does not require a complex calibration process and is therefore likely to produce sharper images than conventionally calibrated systems. Also the invention will be more reliable because it has fewer components to fail and performs fewer operations reducing the possibility of errors and, hence, requires less maintenance.
The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description of the preferred embodiments which make reference to the several figures of the drawing.